This invention relates to control rod drives for nuclear reactors, particularly to such drives for "scramming" the control rods should an emergency occur, and more particularly to a simple, reliable, fast-acting means for releasing a control element and allowing it to be inserted rapidly into the core region of a nuclear reactor for scram or fast shutdown purposes.
The use of control rods and asssociated drives to regulate the reactivity of a nuclear reactor by varying the location of the control rods with respect to the reactive core is well known. Various types of control rod drive systems utilizing releasable gripping or latch mechanisms have been developed, as exemplified by U.S. Pat. No. 3,139,384 issued June 30, 1964 and U.S. Pat. No. 3,604,746 issued Sept. 14, 1971. In general, such drives are capable, under normal conditions, of gradually inserting and withdrawing one or more associated control rods so as to regulate the power output of the reactor. With a view toward the possibility of an emergency condition arising, as by an unexpected rise in reactivity, such drives also generally include arrangements for scramming the control rods, i.e., for rapid full insertion of the control rods into the reactive core to quickly shutdown the reactor. U.S. Pat. No. 3,089,839 issued May 14, 1963, and U.S. Pat. No. 3,575,804 issued Apr. 20, 1971 exemplify prior art control rod scram systems.
With the advent of the liquid metal fast breeder reactors (LMFBR), a need for faster, less complex, more reliable control rod scram or shutdown systems has become apparent, whereby the reactivity of the reactor can be quickly controlled by rapid insertion of the control rods into the reactor core. Furthermore, the unique friction and wear characteristics of structural metals in a high temperature liquid sodium environment require that the mechanisms be designed to be insensitive to changes in friction coefficient and operate over the widest possible range of friction coefficients.